Trigger pull for small arms



July 22, 1947. J. F. McCASLlN 4 2,424,247

TRIGGER PULL FOR SMALL ARMS Filed Feb 1, 1945 /0 AMMm/m r Patented July22, 1947 UNlTED srares rarest (Granted under the act of March 3, 1883,as amended April 30, 1928; 370 0. G. 757) Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment to me ofany royalty thereon.

This invention relates to trigger pull arrangements for small arms suchas rifles, pistols, revolvers, shotguns and the like, and moreparticularly, to arrangements for securing a creepless trigger pulleffect, similar to the efiect obtained in breaking a brittle rod.

A main object of this invention, therefore, is to provide a method andmeans for obtaining a creepless trigger pull for small arms.

A further object of this invention is to provide a method and means forobtaining a creepless trigger pull for small arms by utilizing amagnetic field to produce the quick breakaway efiect.

Further objects of this invention will appear from the followingdescription and claims, and from the accompanying drawings, wherein:

Figure 1 is an elevational view with parts broken away of a portion of arifle mechanism employing a trigger pull arrangement in accordance withthis invention.

Figure 2 is a partial view similar to Figure 1 but showing amodification of the trigger pull arrangement adapted to provide slack inthe trigger.

Figure 3 is a detail view partly in cross-section of a modifiedpermanent magnet structure for a trigger pull arrangement according tothis invention.

Figure 4 is an enlarged cross-sectional view taken on line 44 of Figure2.

Figure 5 is a detail view partly in cross-section of a furthermodification of the invention.

It is very desirable in small arms such as rifles, pistols, revolvers,shotguns, and the like, to provide a trigger pull arrangement, where atthe moment of trigger release, the force opposing the pull on thetrigger is very rapidly reduced so as to result in a sharp cleanbreakaway of the trigger mechanism from its retaining structure. Thedesired effect is analogous to the result which would be obtained if thetrigger was held back by a thin brittle rod such as a glass rod and thetrigger pull resulted in the gradual building up of stress in the rod(considered to be acting as a beam) and the sudden rupture thereof,yielding complete release of the trigger. Such a trigger action would beconsidered substantially creepless and would be highly effective.

Since a glass rod construction is obviously impractical in a rifle orother firearm, it is proposed by this invention to obtain the same, or aclosely similar, efiect by distorting the magnetic field surrounding apermanent magnet. Referring to the drawings, Fig. 1 discloses onearrangement where this method of trigger control is shown as applied toa bolt action rifle. In the other drawings, similar reference numerals.refer to parts identified by reference numerals in Fig. 1.

In Fig. 1, the bolt of the rifle is designated by reference numeral I.Bolt I is provided with a cocking lug 2 which is normally engaged, incocking position by one arm 3 of a sear lever A, pivotally supported inthe cavity provided therefor in the rifle. Another arm 5 of scar lever lis engaged by a trip lug 6 formed on the trigger body 1. Upward movementof arm 5 is cushioned by a coiled pressure spring 3 connected betweenthe upper surface of arm 5 and an adjacent stationary wall of thecavity. Spring 8 biases sear lever 4 to a cocking position. Upwardmovement of lug 6 forces arm 3 out of obstructing position with respectto lug 2 and releases bolt l to fire the weapon.

Trigger body 1 is provided with a forwardly projecting paramagnetic arm9 which extends in normal close proximity to a permanent magnet l9 andis biased to this position by a pressure spring H retained in anadjustable cu member l2, threadedly engaged with an external wall of thetrigger housing. Permanent magnet H) preferably having a magnetomotiveforce in excess of that of ordinary permanent magnets is appropriatelysecured to a stationary support member l3 of non-magnetic material suchas wood. Trigger body 1 is made of magnetic material such as soft steel.

When the trigger is pulled, arm 8 is moved away from magnet Hi, and at acritical position where the air gap between arm 9 and magnet l0 reachesa value where the magnetic force on arm 9 cannot balance the pullingforce on the trigger, the initial magnetic field is weakened and themagnetic flux pattern around permanent magnet Iii shifts to a new form.The sudden shift of the magnetic flux pattern leaves the pulling forceon trigger l unopposed and provides the desired sudden breakaway releaseof the trigger,

The amount of pulling force required to produce the desired quickrelease may b regulated by adjusting cup member I2 to provide theoptimum initial pressure of spring on arm 9.

In the embodiment of Fig, 2 means is provided for introducing a certainamount of slack in the trigger action before the sharp breakaway releaseeffect is obtained. In this embodiment the trigger body, designated asI? is pivotally mounted on a pin I8 coaxially with a sear actuatinglever I9. Sear actuating lever I9 is provided with a trip lug 20 adaptedto urge arm of scar lever 4 upwardly to release bolt I when lever I9 isrotated in a clock-wise direction. Sear actuating lever I9 is furtherprovided with paramagnetic arm 2! provided at its end with an integralopen sleeve portion 22 having a lower flange 23. Trigger body I! isprovided with an arm 24 positioned within said open sleeve portion 22and connected to lower flange 23 by a compression spring 25 so that thepull on the trigger is cushioned by spring 25 until said spring goessubstantially solid, whereupon said pull is transmitted to arm 2!. Arm2| is normally positioned by adjustable cup member l2 and spring I I sothat it is closely adjacent to permanent magnet l9. As arm 2| is moveddownwardly by the trigger pull, the sharp release action is obtained asdescribed in connection with the embodiment of Fig. 1.

Fig. 3 discloses a modification of the permanent magnet employed in thetrigger release arrangement according to this invention, said magnetcomprising a horseshoe magnet having arms 26, 21 connected-by magneticyoke, the ends of the arms being of opposite polarity so that a veryhigh flux density is normally obtained through the trigger arm element29 positioned adjacent their end faces. By this arrangement, thebreakaway effect produced by the rapid decay of the initial magneticfield is considerably enhanced. This structure may be employed witheither the embodiment of Fig. 1 or the embodiment of Fig. 2. Thehorseshoe magnet is secured by appropriate fastening means to anappropriate nonmagnetic member 28 forming part of the wall structure ofthe trigger cavity.

Although, as disclosed in the foregoing embodiments the permanent magnetis stationary, the magnet may be instead mounted on the movable triggerarm element and may cooperate with a suitable stationary element ofmagnetic material to produce the desired quick release action. As shownin Fig. 5, the forwardly projecting trigger arm 32, preferably ofnon-magnetic material, has a permanent magnet 3! affixed to its uppersurface. The stationary element 30 is formed of iron or soft steel andis secured by appropriate fastening means to the member 28 forming partof the wall structure of the trigger cavity. It will be understood thatthe modifications of Figs. 1 through 4 may be appropriately modified byplacing the magnet on the movable trigger arm and providing acooperating stationary magnetic element.

While certain specific embodiments of trigger pull arrangements forsmall arms have been disclosed in the foregoing description, it will beunderstood that various modifications within the spirit of the inventionwill occur to those skilled in the art. Therefore, it is intended thatno limitations be placed on the invention other than as defined by thescope of the appended Claims.

What is claimed is;

1. In a device having a permanent magnet mounted in the body thereof anda paramagnetic element, adjustable means for maintaining the saidparamagnetic element normally within the effective flux of saidpermanent magnet and trigger means for manually activating the saidparamagnetic element and moving it to a weaker outer zone of the saidflux.

2. In a firearm having a permanent magnet mounted in the body thereofand a trigger comprising a paramagnetic element, means of subjecting thesaid trigger to the effective magnet0- motive forces of the said magnetin close proximity thereto, said trigger being arranged to manuallyactivate the said paramagnetic element and move it to a point beyond theeffective range of the said magnetomotive forces.

3. Means for obtaining quick release of a firearm trigger comprising apermanent magnet secured to the firearm, a manually operated triggerhaving a paramagnetic element formin a part thereof, said trigger beingarranged to move the said paramagnetic element against the magnetomotiveforces of the said magnet to a point beyond their effective range, andmeans for pcsitioning the said paramagnetic element normally within theeiTective flux of the said magnet.

4. Means for obtaining a quick release of a firearm trigger comprising apermanent magnet secured to the firearm, a manually operated triggerhaving an outwardly extending arm forming a part thereof, a paramagneticsear-operated lever mounted between said magnet and said arm, the saidtrigger being pivotally mounted on the firearm to move the saidparamagnetic lever from a predetermined position within the strong innerzone of the magnetic field of the said magnet to its weaker outer zoneupon activation of the said trigger, resilient cushioning means betweenthe said trigger and the said lever whereby slack is provided in thetrigger action, and means for predetermining the position of the saidparamagnetic element within the inner zone of the magnetic field of thesaid ma net.

5. The structure of claim 4 wherein the paramagnetic sear actuatinglever is provided with an open sleeve portion within which the arm ofthe said trigger may move.

JAMES F. McCASLIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,875,941 Schwartz Sept. 6, 19322,293,957 Wells Aug. 25, 1942 2,331,405 Loomis Oct. 12, 1943 2,274,195Garrison Feb. 24, 1942 1,146,637 Massa July 13, 1915 1,534,753 WatsonApr. 21, 1925 2,188,803 Boehne Jan. 30, 1940

